Interlocking blocks are known and there have been many proposals in the past, the closest prior art of which I am aware being the publication of International Patent application No. PCT/GB80/00069 in which I am named as an inventor. Further prior art of which I am aware are the disclosures in the following Patent specifications.
United Kingdom Pat. No. 577052 PA1 United Kingdom Pat. No. 591067 PA1 United Kingdom Pat. No. 654057 PA1 United Kingdom Pat. No. 788652 PA1 Swiss Pat. No. 350453 PA1 French Pat. No. 1135128 PA1 French Pat. No. 56908 (Addition to No. 1002508) PA1 French Pat. No. 1002508 PA1 French Pat. No. 1209309 PA1 French Pat. No. 1312989 PA1 French Pat. No. 905471 PA1 International Patent application Publication No. WO79/00198.
The earlier specification No. PCT/GB80/00069 discloses a building block comprising an inner wall and a spaced, parallel outer wall, at least one web connection between the inner and outer walls, an offset face on said outer wall, said face being offset vertically to provide a projecting extension along the greater part of a horizontal edge of the outer wall, and a rebate along the greater part of the opposed horizontal edge of the outer wall whereby one block may interengage with adjacent blocks above and below, the offset face being so arranged, by the provision of the projecting extension being smaller in depth than the corresponding rebate and the projecting extension and the rebate each having a generally vertically extending inner wall, one of which has a contoured surface portion facilitating interengagement of a projecting extension and a cooperating rebate, that the offset face merely locates the block where the load is transmitted through the inner and outer walls.
Whilst that form of block is technically satisfactory I have found in practice that it is susceptible to damage and requires to be made to extremely close tolerances whereas the block of the present invention transmits the load through the outer sections of the block so that they are thicker and resist damage. Moreover, with the standard block, if damage does occur to one face of the block the block can be turned through 180.degree. to present the other face to the outside. Similar objections relate to the other prior art mentioned above, for example: United Kingdom Patent specification No. 577052 illustrates a moulded block formed of three vertical parallel and spaced layers, the intermediate layer projecting beyond the outer layers, at one end and at the top or bottom, and being inset at the other end and at the top or bottom so that adjacent blocks will interlock. However, in that arrangement the block is complicated to mould and the location is provided by the same portions of the block as those which transmit the load.
United Kingdom Patent specifications Nos. 591067 and 788652 both illustrate similar blocks to the invention disclosed in our previous specification having an offset locating face with load transmit through the inner and outer walls. However, in both disclosures the projecting portions are intended to compliment the rebates. Whilst such an arrangement is satisfactory where the tolerances can be controlled exactly in practice this cannot be done. This has the result that in some blocks where tolerance variations exist the load will be transmitted only through the locating face and not through the block as a whole, thus producing a weakened structure. Also including such a variation will cause the block to be positioned incorrectly, an error which will become exaggerated as a structure is built with such blocks and cannot readily be corrected.
United Kingdom Patent specification No. 654057 discloses another block of this type having an offset locating face providing projecting portions and corresponding rebates which are arranged to leave a narrow gap between adjacent edges of the blocks. These gaps increase the labour requirement since they have to be filled with mortar or cement to ensure a firm structure. However, whilst the gaps will aid in seating the blocks one on another, the offset faces are still susceptible to damage and tolerance variations cannot be accommodated.
Swiss Patent specification No. 350453 discloses building bricks which makes it possible to interlock horizontally and vertically so that a strong structure may be produced. However, the arrangement has opposed male and female end connectable portions so that identically constructed building elements may interlock with one another.
French Patent specification No. 1135128 discloses a similar type of building block which is characterized by a special shape consisting of a cavity with a recess and a boss on two opposing faces. The recess and the boss are complimentary so that two identical bricks may be interlocked.
French Patent Of Addition No. 56908 and its parent Pat. No. 1002508 discloses a block which interlocks from above and below and at each end. However, the blocks are male at one end and female at the other so that they cannot be turned around. Moreover, the blocks proposed are of a complicated configuration making it difficult to mould, and susceptible to tolerance variations.
French Patent specification No. 1029039 is similar to our earlier specification in disclosing male and female interlocking. However, this prevents the problems discussed above.
French Patent specification No. 1312989 is yet another block in which interengagement is from above and below and at each end but with opposed male and female end portions so that the blocks can only be used one way around.
International Patent specification WO 79/00198 discloses a block in which the load is transmitted through the outside of the block. However, the block discloses male and female end portions which will not permit reversal of the block in the present of tolerance variations.